In vehicles, a transmission is equipped for converting the power from the engine according to the driving state of the vehicle. As a transmission, there are a manual transmission to manually change gear engagement, and an automatic transmission to automatically change engagement according to the driving state of the vehicle.
The manual transmission is equipped with a plurality of gear trains and gear-shifting mechanisms for the gear trains. The gear-shifting mechanism is manually operated so that one of the gear trains is engaged. In contrast, the automatic transmission is typically equipped with a torque converter and an auxiliary transmission. An actuator switches the engagement of the auxiliary transmission based on the position of a shift lever.
In addition, there exists an automatic transmission based on the manual transmission having gear trains and gear-shifting mechanisms so as to change the gears automatically. FIG. 7 shows such automatic transmission, where reference numeral 302 designates an engine and 304 an automatic transmission.
The automatic transmission 304 comprises an input shaft 310 connected to a crankshaft 306 of the engine 302 on the vehicle (not shown) through a main clutch 308, an output shaft 312 connected to a drive wheel (not shown), and first through fifth speed gear trains 314, 316, 318, 320, 322 and a reverse gear train 324. The gears transmit the driving power from the input shaft 310 to the output shaft 312 at different ratios.
The gear trains 314, 316, 318, 320, 322 and 324 are changed by the gear-shifting mechanism. The gear-shifting mechanism of the automatic transmission 304 includes a first-to-second shifting mechanism 326, a third-to-fourth shifting mechanism 328, a fifth speed shifting mechanism 330, and a reverse shifting mechanism 332. Reference numeral 334 designates a final reduction gear train, 336 a differential gear, and 338 a driving shaft in connection with a drive wheel (not shown).
In the automatic transmission 304, an automatic shift controller (not shown) switches the gear engagement automatically. The automatic shift controller controls an actuator (not shown) to operate the gear-shifting mechanisms 326, 328, 330, and 332 so that one of the gear trains 314, 316, 318, 320, 322 and 324 is engaged according to the position of a shift lever (not shown).
Examples of the controllers are disclosed in JP Laid-Open No. 2001-227600 and JP No. 2000-97297 Official Gazettes.
The controller disclosed in JP Laid-Open No. 2001-227600 comprises: an input shaft; a main clutch to transmit driving power of the engine to the input shaft; a counter shaft to which the driving power from the input shaft is transmitted through the gears; an output shaft to transmit the driving power to a rear differential, which shaft is disposed on an axis in a direction of the input shaft; an intermediate shaft on an axis other than the input shaft and the counter shaft; and a sub-clutch on the intermediate shaft. The sub-clutch variably controls the torque transmitted from the input shaft to the output shaft during gear change.
The controller disclosed in JP Laid-Open No. 2000-97297 comprises: a first drive shaft supported in a transmission housing; drive gears rotatably mounted on the first drive shaft; a second drive shaft concentric with the first drive shaft; drive gears rotatably mounted on the second drive shaft; a driven shaft in parallel with the first and second drive shafts; and a driven gear fixed on the driven shaft and in mesh with the corresponding drive gear on the first and second drive gears.
A normal automatic transmission with a torque converter (AT with torque converter) includes a parking mechanism having a parking gear. Referring to FIG. 6, the vehicle of the normal automatic transmission is parked in which the parking mechanism allows the parking gear to be engaged when the shift lever is in a parking position.
In contrast, an automatic transmission based on a manual transmission MT does not have “a parking state” by which the shift lever is in the parking position as in the normal automatic transmission with the torque converter.
This is due to that, as shown in FIG. 6, for the automatic transmission based on the manual transmission (automatic MT), the vehicle is parked, i.e. stopped, while utilizing stop of the engine, or stopping force of the engine, in which the gear train, e.g. reverse gear, and the main clutch are engaged respectively while the engine is stopped as in the manual transmission.
At or after engine start-up, the vehicle with the conventional automatic transmission based on the manual transmission cannot be in the parking state, since the stop of the engine cannot be utilized.
On this account, the conventional automatic transmission based on the manual transmission requires a separate parking mechanism such as a parking gear to achieve and maintain the parking state at or after engine start-up. The parking mechanism should be communicated with the shift lever through select cables for mechanical operation, which results in cost increase.
Also, in starting-up the engine in the parking state with the gears engaged, the engine starts up and at the same time the parking state is cancelled. Therefore, it is required to determine from signals such as a brake signal whether the vehicle is able to move. If it is determined that the vehicle is able to move, the engine is prevented from start-up. On this account, if the time between the determination and the engine start-up operation is not enough, control may not work properly, which results in problem of startability.